The present invention relates to bearing inserts for operably supporting a rotatable shaft, such as a cam shaft in an internal combustion engine, and further relates to a method for repairing spaced-apart bearing supports to receive the bearing inserts, and still further relates to a broaching tool for use in the method.
Modern internal combustion engines for passenger vehicles typically include a cylinder head and a cam shaft rotatably supported at journals by the cylinder head at multiple aligned bearing locations. The cylinder heads include a bearing support structure (sometimes called "bearing housings") at each of the bearing locations. An oil port is included in each bearing support structure for passing oil to journals on the cam shaft. As engines age, the bearing surfaces on the cylinder head and the journals on the cam shaft wear, such that these bearing locations sometimes need to be rebuilt. In extreme cases, galling and material deformation may occur, causing the cam shaft to roughly rotate or even freeze up on the cylinder head. It is known to repair these bearing locations by welding on the cylinder head to reapply material to the support structure, and thereafter to machine away excess material to reform the bearing surfaces. It is also known to simply machine away material on the cylinder head to form an oversized bearing surface. A problem is that accurate alignment of the bearing locations along a cam shaft is very important so that the cam shaft is properly positioned for rotation without stress, and so that the intake and exhaust valves of the internal combustion engine work properly. Set up for good alignment to recut the bearing locations is expensive and time consuming and can easily be done wrong. Further, the tools for cutting and machining the bearing locations can be expensive. Also, a plurality of different tools is required for each different bearing size, such that it requires significant capital investment for a repair shop. There are also the frustrations of not having (or not being able to find) the right size cutting tool for a particular size bearing.
It is known to cutaway the bearing support structure and to locate a whole new massive outer bearing in the cylinder head to support the cam shaft. Further, it is known to purchase new replacement cam shafts having particular sized cam shaft bearing surfaces. However, it is undesirable to cutaway substantial material from the cylinder head of modern engines since this can affect their strength, operation, and heat flow in the cylinder head in adverse ways. Further, removal of large amounts of material can lead to mistakes that totally destroy cylinder heads.
Notably, inserts have been used on valve guides for supporting linear movement of intake and exhaust valves on internal combustion engines for many years. For example, see U.S. Pat. Nos. 4,768,479 and 5,249,555. However, despite this type of engine repair for several years, no one has, to the inventor's knowledge, ever conceived of using thin-walled inserts in cam shaft bearings because different problems are presented. One such problem is that existing cam shaft constructions require that oil be injected from a side of the cam shaft bearing area so that oil reaches and lubricates the journals of the cam shaft. Further, it is difficult to retain a thin-walled insert in a cam shaft bearing arrangement due to the torsional forces on a cam shaft bearing, both in terms of preventing rotation of the insert and also preventing longitudinal creeping of the insert during use.
Accordingly, there is a need for a reliable bearing insert and a related method and tools that solve the aforementioned problems and that have the aforementioned advantages.